A conventional press apparatus used for squeezing water from a wet paper web in a papermaking process has four press nips, and is shown in FIG. 1.
A wet paper web W, having a density of 15–18%, formed in a wire part of the papermaking apparatus, is sucked onto a suction pickup roll 2 and attached to a pickup felt 3. Water is squeezed from the wet paper web through the felt 3, and a bottom felt 4, in a first press 1P which is referred to as a “double felt press,” since it comprising two felts 3 and 4, as well as a suction roll 5 and a grooved roll 6a. 
The wet paper web is held on the surface of the pickup felt 3, and sucked by vacuum of the suction roll 5. Water is further squeezed from the wet paper web in a single felt press 2P, which comprises a center roll 6, having a dense, smooth surface, and a grooved roll 6b. 
Rewetting of the wet paper web W, that is, the return of water from the press felt to the wet paper web, occurs in this process where the wet paper web is transferred from the first nip formed by rolls 5 and 6a, to the second nip formed by rolls 6 and 6b. 
After the pickup felt 3 transfers the wet paper web W to the center roll 6, water is squeezed from the wet paper web in a third press 3P, comprising the roll 6 and a third grooved roll 6c, and in a fourth press 4P, comprising a roll 7 and a grooved roll 6d. Thereafter, the wet paper web is transferred to a dryer part of the papermaking apparatus, comprising dryer rolls 8.
A double felt press nip is shown in detail in FIG. 2. The press nip comprises a pair of press rolls P, and a pair of press felts 11, which pinch a wet paper web W. The press felts 11, and the wet paper web W, are compressed by the press rolls P, and thus water is squeezed from the wet paper web W.
While FIG. 2 shows a roll press wherein a nip comprises two rolls, alternatively, a shoe press may be used, in which the nip comprises a roll and a shoe press module. In the shoe press, as in the roll press, press felts absorb water squeezed from a wet paper web.
The structure of a press felt 11, of the kind generally used in papermaking, is shown in FIG. 3, which is a cross-sectional view taken on a plane extending in the machine direction. The felt 11, shown in of FIG. 3, is an endless press felt, comprising a base body 20 and layers 30 of batt material. The batt material comprises a wet paper web side layer 31 and a press side layer 32. The batt material is formed by needle punching a batt fiber to the base body 20. Thus, batt fiber is provided inside the base body 20.
The movement of water from the wet paper web in the press part of FIG. 2 is illustrated in FIG. 4. For simplicity, only one press felt 11 is shown in FIG. 4. When the two press rolls P rotate in the directions shown by the arrows in FIG. 4, the press felt 11 and a wet paper web W are pinched by the press rolls P as they pass through the press part. As mentioned above, the press felt 11, and the wet paper web W, are compressed in the press part, and water is squeezed out of the wet paper web W and absorbed in the press felt 11.
However, when the wet paper web and the press felt are transferred from the center of the nip to the delivery side of the press part, the pressure applied to the wet paper web W and the press felt 11 is rapidly released, and the press felt 11, and the wet paper web W, rapidly expand in volume. As a result, a negative pressure is created in the press felt 11. Moreover a capillary phenomenon occurs, since the wet paper web comprises thin fibers. The negative pressure and the capillary phenomenon cause water absorbed in the press felt 11 to return to the wet paper web W. This “rewetting” phenomenon and is generally known by those skilled in the art as a problem in a conventional press apparatus.
While FIG. 4 shows a case of a roll press nip, the same phenomenon occurs in the case of a shoe press nip. In both types of press nip, rewetting is a major cause of decreased water removal capability.
One conventional press felt designed to reduce rewetting, is shown in FIG. 5, and described at page 3 of Unexamined Japanese Patent Publication 8888/1991. In this press felt, a barrier layer 41, comprising super-fine fibers or a hydrophilic material, is formed in a press side part 32 of the batt material.
In another conventional press felt, shown in FIG. 6 and described in U.S. Pat. No. 5,372,876 a hydrophobic spun bond layer 42 is provided as part of the wet paper web side part 31 of the batt material.
The results of experiments have revealed that the structures shown in FIGS. 5 and 6 did not sufficiently prevent rewetting. The inability of press felt 12 of FIG. 5 to prevent rewetting appears to be due to the fact that, while water is held in the barrier layer 41 comprising super-fine fibers or hydrophilic material, water in the wet paper web side layer 31, which lacks the barrier layer material, returns to the wet paper web after the press felt is released from the press part of the machine.
In the case of the press felt 13 of FIG. 6, the hydrophobic spun bond material 42 prevents water which is located on the roll side relative to the spun bond material from moving to the wet paper web. However, the press felt of FIG. 6 does not function effectively to prevent rewetting, apparently because, since the spun bond material 42 is hydrophobic, water held inside the spun bond material, and water located in the batt layer on the wet paper web side of the spun bond material, move easily to the wet paper web.
In view of the above problems, it is an object of the invention to provide a papermaking press felt and a press apparatus which more effectively prevent rewetting.